While the invention is subject to a wide range of applications, it is especially suited for services such as water, sewage, and other liquids, as well as slurries which cause leakage or plugging in a simple check valve and will be particularly described in that connection.
It is a common practice to provide a pump check valve in a pumping system in order to prevent backflow to the pump and assure positive flow control. The valve is located between the pump and the system which receives the pump fluid. By keeping the valve closed during start up, the pump need not work against system pressure or backflow. This pump check valve can also reduce the possibility of water hammer and surge throughout the system. Water hammer and surge occur because in preventing backflow, the valve must be kept closed while the pump is brought up to a discharge pressure which is higher than the pressure in the system downstream from the valve. When the valve is then opened, the high discharge pressure contacts the lower system pressure and can cause water hammer and surge. Pump check valaves generally use controls to open and close in relation to the pump output. Up to now, pump check valves have not consistently eliminated water hammer and surge.
The prior art use of pump check valves can be described as follows: A decrease in system pressure or liquid level causes a switch to start the pump motor, and the discharge pressure of the pump begins to rise. After the pump discharge pressure reaches system pressure, another pressure switch energizes the valve actuator and the valve begins to open at a preset speed. As the pump output increases, the valve continues towards its fully open position. Finally, the pump reaches 100% capacity at the same time that the valve is fully open. This not only prevents pressure build-up at the valve, but also prevents any backflow to the pump.
The prior art closing cycle commences when a pressure or level requirement in the system is satisfied and a signal is transmitted to the pump check valve which begins its closing cycle at a preset speed. When the valve reaches a predetermined partially closed position, the pump is turned off. The valve continues to close as the pump slows down. Finally, the valve is supposed to close just as the forward flow from the pump stops.
The prior art system described above depends on an external and remote device, not correlated with the operating characteristics of the pump or the valve, for controlling the actuation of the system. Prior art devices have not been ale to consistently eliminate the problem of water hammer and surging in piping systems. In piping systems of large diameters and/or systems of high pressure, the elimination of water hammer and surging becomes extremely important as this phenomena can actually tear apart a valve or a pipe and can therefore prove to be very costly.
In addition, prior pump check valve systems require very lage actuators to develop the high torque necessary for rotating the valve against a high downstream pressure.
It is an object of the present invention to provide a method and apparatus that eliminates pressure surging and water hammer.
It is a further object of the present invention to provide a method and apparatus that maintains constant pressure in the system during the entire opening cycle of the valve.
It is a further object of the present invention to provide a method and apparatus that delivers fluid to the system when the pressure differential across the pump check valve is substantially zero.
It is a further object of the present invention to provide a pump check valve control apparatus whose valve port is fully open just as the pump reaches full discharge pressure.
It is a further object of the present invention to provide a pump check valve control apparatus whose valve port is fully closed just as the discharge pressure of the pump is substantially equal to the pressure of the system.
It is a further object of the present invention to provide a pump check valve control apparatus whose actuator requires a low torque to open.